The present finding relates to die-casting machines. In particular, it refers to a piston of a press for die-casting.
Die-casting machines can be of the hot chamber or cold chamber type.
An injection piston is commonly used in hot chamber die-casting machines, having a steel body with sharp or slightly bevelled edge head carrying one or usually two copper alloy sealing bands spaced in parallel from one another and from the piston head.
In cold chamber die-casting machines, both the use of an injection piston with a copper alloy or steel body without outside sealing bands and with an optional peripheral head step and/or bevel, and the use of an injection piston with a copper alloy body and an outside sealing band arranged astride of a collar at the piston head, are known.
Such known embodiments, however, exhibit the disadvantage of a relatively quick loss of seal, and thus, a reduction of the piston efficiency and life following the wear, especially of the sealing band closer to the piston head, which is also increased by thermal deformations of the system, such as ovalization of the piston container. In this case, the seal can only be restored by replacing the worn band or bands.
A purpose of the present finding is that of providing a piston for cold chamber die-casting which should be more efficient and with a longer life than the current ones, and which should thus allow reducing the operating costs of die-casting machines.
Another purpose of the finding is that of proposing a piston provided with sealing bands in copper alloy which, even though becoming worn, should be stressed to rearrange radially and conform to the thermal deformations, so as to not impair the piston life and efficiency.
Such purposes are achieved by a piston for cold chamber die-casting machines comprising a steel body having a head with or without peripheral bevel and at least one sealing band in copper alloy arranged around the body into a respective housing obtained in back position with respect to the head, and where at least two channels are obtained on the outside surface of the piston comprised between head and band, suitable for placing the piston head in communication with the annular housing of the band, for an inflow of metal under the same band.
In this way, when the metal flowing to the housing solidifies, it creates a continuous thickening which radially pushes the band outwards, thus progressively recovering its wear, conforming it to the possible deformations of the container of the piston and thereby protecting the latter.